A laser-plasma base synchrotron radiation source

A number of new methods have been proposed of late to produce X-ray photons with high brightness and short pulse duration, namely extremely high order harmonics from a laser, inverse Compton scattering and laser plasma acceleration. Dr. S. Kneip and his colleagues have recently applied the last of these types of technology to a table top synchrotron X-ray source. The method uses the phenomenon whereby the passage of an intense laser pulse through an underdense plasma generates a so-called plasma wakefield, which can have intrinsic fields of 1,000 times or more the best achievable by conventional accelerator technology. Some readers might recall previous news articles, "Table-top soft X-ray undulator source" in X-ray Spectrometry, Vol. 39, No.1 (2010) and "A compact synchrotron light source driven by pulse laser", in X-ray Spectrometry, Vol. 37, No.2 (2008). Both are pioneering reports on wakefield-driven synchrotron radiation. After generating high-energy electrons by laser pulse, they tried to transport the beam to an undulator, which is a magnet array and usually known as an insertion device placed at the straight section of the storage ring. In contrast, the electron beam in the plasma accelerator undergoes transverse (betatron) oscillations when subject to the focusing fields of the plasma wave, and the radiation wavelength can extend to the hard X-ray region as well. The research group succeeded in enhancing the brilliance of this betatron radiation by optimizing the wakefield conditions. They were able to accelerate electrons upto 230 MeV with a 5 mm path, and the critical energy of the obtained radiation was 6-10 keV. For more information, see the paper, "Bright spatially coherent synchrotron X-rays from a table-top source", S. Kneip et al., Nature Physics, (2010) (Published online, DOI:10.1038/nphys1789).